In the development of the hold-type display, such as a liquid crystal display (LCD) organic light emitting diode (OLED), because of the advantages of low power consumption, easy installation, and good future development, the hold-type display has been widely used in technical fields and is popular among consumers. Therefore, the development of the hold-type display will move toward more complete electrical characteristics of a wider display area and better display quality, etc.
However, the display quality of hold-type displays is worse than that of cathode ray tubes (CRTs), because there is a difference between the display theorem of hold-type displays and that of CRTs.
Generally, the display theorem of a CRT is that the input electronic display signal is transformed into an enhanced electron beam and then restored to image by deflective scanning and screen. In other words, the contrast, color, gray level of display image will be obtained according to a scan with the electron beam. Referring to FIG. 1, FIG. 1 is a diagram depicting a brightness signal vs. time for a conventional CRT display, wherein the brightness signal 10 is a continuous time-dependent pulse. Referring to FIG. 2, FIG. 2 is a spectrum diagram showing the brightness signal processed by Fourier Transformation for a conventional CRT display according to FIG. 1. As shown in FIG. 2, when the amplitude signal 12 is maintained stably within the cutoff frequency 14 or continuously at a horizontal status, the blurring of a moving image is not visible, since it is not sensitive for human eyes to receive the display image whose frequency is over the cutoff frequency 14 (generally about 60 Hz).
On the other hand, the display theorem of a hold-type display, such as an LCD, is different from the display theorem of a CRT. The display theorem of an LCD is to twist the liquid crystal by bias to block light, or to let light go through, because the liquid crystal of an LCD cannot emit light by itself. Then the light will pass through the color filter to have different colors. Referring to FIG. 3, FIG. 3 is the diagram depicting a brightness signal vs. time for a conventional LCD, wherein the brightness signal 10 is a continuous time-dependent curve. Referring to FIG. 4, FIG. 4 is a spectrum diagram showing the brightness signal processed by Fourier Transformation for a conventional LCD according to FIG. 3. When the amplitude signal 22 cannot be maintained stably within the cutoff frequency 24, and declines at the cutoff frequency 24 as shown in FIG. 4, human eyes will sense a blurred image apparently, especially for a motion image, because human eyes are sensitive to the image whose frequency is within the cutoff frequency 24.
Referring to FIG. 5, FIG. 5 is another diagram depicting a brightness signal vs. time for a conventional LCD. The brightness signal 26 as shown in FIG. 5 is affected due to the slow rotation of LC molecules. FIG. 6 is a spectrum diagram showing the brightness signal processed by Fourier Transformation for a conventional LCD according to FIG. 5. The amplitude signal 28 as shown in FIG. 6 will decline quickly at the cutoff frequency 30, because the brightness signal 26 of FIG. 5 is affected by the parasitic capacitance, RC delay etc. Therefore, the image will be more obscure.
Referring to FIG. 7, FIG. 7 is a diagram of display time vs. display position for a conventional impulse-type display, and meanwhile, referring to FIG. 8, FIG. 8 is a diagram of display time vs. display position for a conventional hold-type display. Because the liquid crystal of an LCD acts like “a switch of light” for controlling the transmittivity of light, there will be a time delay between “open” and “close” of “the switch of light” because of the slow response of the liquid crystal. Thus, there will be a residual image in the display, and the contrast will decrease.
In FIG. 7 and FIG. 8, the path of display character of pulse-type display is almost continuous, and the path of display character of hold-type display is like a stair. By further comparing FIG. 1, FIG. 2 and FIG. 3, FIG. 4, after the display signal is processed by Fourier Transformation, the amplitude of display signal of pulse-type display is maintained horizontally and stably in accordance with frequency, and the amplitude of display signal of hold-type display is a continuous wave depending on frequency, although the same signal is displayed. Thus, the image quality of hold-type display is worse than the image quality of pulse-type display, because there are blurring image in hold-type display in high frequency within the time domain.
Referring to FIG. 9, FIG. 9 is a diagram showing the comparison between the transmissivity of an LCD and the brightness property of a CRT. In FIG. 9, the curve of the brightness property of a CRT rises gradually. In other words, any brightness and gray level are controlled by a continuous voltage. However, regardless of the normal black display mode and the normal white display mode, the curve of the transmissivity of an LCD is like an “S”. There is the threshold voltage 50 in the normal black display mode, and there is the threshold voltage 60 in the normal white display mode. When the control voltage achieves the threshold voltage, the change of transmissivity will begin. In FIG. 9, it is shown that the action of a liquid crystal of an LCD is like “a switch of light”, because the light will pass if the “switch” opens, and the light will be blocked if the “switch” closes.
Referring to FIG. 10, FIG. 10 is a flow sheet of the conventional image process. First, a display signal 70 is provided and will be transformed to a digital signal 74 at a signal receiver 72 after an amplification process, a filter process and a sampling process. Then the digital signal 74 is transferred to a display signal adjuster 76 for image compensation and adjustment, and the optimum display signal will thus be obtained. Afterwards, a driving signal 80 transformed from the optimum display signal by utilizing a decoder and driver 78 will be outputted to a monitor 82, so that human eyes 84 can see the image of the display signal 70.
Recently LCD is used widely in all respects, but the dynamic display quality of an LCD is worse than the dynamic display quality of a CRT. In order to enhance the dynamic display quality of a hold-type display, such as an LCD and an OLED, many methods are applied. For example, a compensation or correcting module is added to enhance the dynamic display quality or to speed up the response time of the liquid crystal in a conventional image process.
However, a lot of improved methods are aimed at the static V-T (voltage-time) curve of an LCD, and the interactive relation between the dynamic response between liquid crystal of an LCD and human eyes is ignored. The driving process of liquid crystal of an LCD consists of a series of fast action in the liquid crystal, so that the response of the liquid crystal is dynamic in different surroundings, such as different temperature, different humidity etc. Therefore, the efficacy of the conventional method for improving the dynamic display quality is limited. The dynamic display quality can only be improved slightly by speeding up the response speed of the liquid crystal of an LCD, and there is still a limitation to the response speed of the liquid crystal. Besides, the cost and difficulty of implementation is higher, so that the cost of the product will increase.